1. Field of the invention
The present invention relates to a fuel vapor control apparatus for restraining fuel vapor from flowing out of a fuel tank.
2. Description of the Related Art
Fuel vaporization is promoted in a fuel tank when a space containing a relatively large amount of air exists over a surface of liquid fuel in the fuel tank. The fuel tank is connected to the atmosphere to allow the surface of liquid fuel to readily lower as fuel in the fuel tank is consumed. Therefore, fuel vaporizes in the fuel tank and fuel vapor flows out into the atmosphere, which is environmentally unfavorable. A related-art technology for reducing an amount of fuel vapor that flows out of the fuel tank into the atmosphere by cooling the fuel vapor to liquefy it and return it to the fuel tank is disclosed in, for example, Japanese Patent Application Laid-open No. HEI 6-147029.
In the technology disclosed in Japanese Patent Application Laid-open No. HEI 6-147029, the amount of fuel vapor is temporarily reduced by cooling fuel vapor extracted from the fuel tank to condense and return it to the fuel tank. However, corresponding to the reduced amount of fuel vapor, fuel vapor is generated in the fuel tank, and again flows out of the fuel tank. Therefore, it is necessary to control fuel vaporization in the fuel tank in order to restrain the outflow of fuel vapor from the fuel tank. Since fuel more readily vaporizes as the temperature in the fuel tank becomes higher, the fuel tank temperature needs to be kept low in order to restrain fuel vaporization. Therefore, in order to restrain fuel vaporization in a conventional fuel tank, energy is needed in large quantities to maintain low temperatures in the fuel tank.